Separation of acetylene from gas mixtures



Jan. 27, 1959 E. BARTHOLCME' ET AL 2, 7 7

SEPARATION OF ACETYLENE FROM GAS MIXTURES Filed Jan. 25, 1956 2 She ets-Sheet 1 FIG. I G v "I Z WASHING TOWER RECTIFICATION DEGASSING 2 sTAsE rowan A rowan [L EXPANSION F VALVE 2 COMPRESSOR l r WASHING I rgwsn D I STAGE 2 E I o B 2 H ACETYLENE Q- CONTAINING 1 GAS A Q N 2 -PsTAsE G RECTIFICATION M p F|G 2 WASHING TOWER h TOWER EXPANSION DEGASSER (VALVE J'\ A I a v Z I 1 T c A |I STAGE wa E I I 0 B r ACETYLENE LU, coummme A K A GAS A v y Y J u A INVENTORS:

ERNST BARTHOLOME OTTO FREY ERWIN LEHRER' LOTHAR LORENZ ATT'YS Jan. 27, 1959 E. BARTHOLOMEJ ET AL 2,

SEPARATION OF ACETYLENE. FROM GAS MIXTURES Filed Jan. 25, 1956 2 Sheets-Sheet 2 FIG. 3

RECTIFICATION P 2 D STAGE ii TOWER DEGASSER WASH'NG EXPANSION TOWER VALVE-IN 1 sues WASHING 1' k rowan O x K W ACETYLENE couumme GAS A v x INVENTORS: ERNST BARTHOLOME' OTTO FREY ERWIN LEHRER LOTHAR LORENZ IQOI m d am MT ATT YS 2,870,867 Patented Jan. 27, 1959 SEPARATION OF ACETYLENE FROM GAS MIXTURES r Ernst Bartholome, Heidelberg, Otto Frey, Ludwigshafen am Rhine, Erwin Lehrer, Bad Duerkheim, and Lothar Lorenz, Ludwigshafen am Rhine, Germany, assignors operates under pressure, the washing can be carried out at this pressure or a slightly higher pressure.

to Badisehe Anilin- & soda Fabrik Aktiengesellschaft,

Ludwigshafen am Rhine, Germany Application January 25, 1956, Serial No. 561,205

Claimspriority, application Germany January 27, 1955 7 Claims. (Cl. 185-115) l The present inventionrelates to, an improved method of separating acetylene from gas mixtures. i

For the separation of acetylene from gas mixtures, in

particular those which have been obtained by. thermal or electrical cracking of hydrocarbons with or without oxygen, processes are knownaccording to which the acetylene is washed out from the gas mixture by a solvent. order to be able to absorb the largest possible amounts of acetylene, this washing is carried outunder increased 1 pressure. If the gas is put under pressure, however, difli- .culties are encountered, chief among which are the following: black deposits will form on the suction valves of the compressor and affect the functioning of the valves after some time; incrustations of more or less dark coloration will form in the cooling devices of the compressor, reduce the cooling effect and even clog the condenser tubes after some time. These incrustations can only be removed by mechanical means. According to our knowledge these incrustations partly consist of polycyclic hydrocarbons, as for example naphthalene, B-methylnaphthalene, acenaphthene, and acenaphthylene. The said shortcomings can be remedied by subjecting the gas to a pre-wash treatment with a solvent capable of absorbing second stage the pressure is higher; it may lie for example between about 8 and 30 atmospheres.

tions, the quantities of solvent tobe circulated beingtoo large when employingtoo low a pressure. pressure limit is determined by. the necessity for. the partial pressureof the acetylene being not higher than that to which lacetylene can be compressed without danger of explosion. The pressure limits, as a result, are also determined by the composition of the gas mixture, ire.

by the percentage of acetylenes. The amount of washing liquid which is first stage is only a small fraction of the washing liquid which is. used in the main washing in the second stage. a As a rule, for the preliminary washing in the first stage,

less than 2% of the amount of washing agent used in the second stage is sufficient. The amount of solvent used in the first stage is preferably an amount just sufficientto recover substances harmful to. high-pressure operation while absorbing onlya small quantity of acetylene and a minor part of the diacetylene presentin the gas mixture. Optimum quantities of solvent can be readily determined by simple experimentation. To obviate the said difli culties the said polycyclic hydrocarbons which melt at a temperature lying above that of the cooling water used, need only be washed out to such an extent that the temperature under the prevailing pressure conditions, does not fall below the dew point.

Solvents suitable in the practice of our invention are such organic. solvents with a boiling point higher, for example, than 150 C. and a high solvent power for acteylene, as are stable thermically and at least partially miscible with water, as for example butyrolactone and liquid is elfected in the usual way by releasing the presthe said contaminants. Thus, it has heretofore already been proposed to strip the gas of diacetylene with a solvent prior to compression. Wherever solvents have been used for a pre-wash of a gas, they had to be stripped from the gas separately in order to be re-used in a cycle.

We have now found that the separation of acetylene can be carried out in a simpler manner while avoiding the said disadvantages and with only one solvent by working in two stages, a smaller amount of the solvent being used in the first stage at atmospheric pressure or at the pressure at which the gas mixture is formed or slightly above the same, and a larger amount of the same solvent being used in the. second stage at a higher pressure than in the first stage. The washing liquids are freed from the absorbed substances in the usual way by releasing the pressure and degassing, preferably at elevated temperature and sub-atmospheric pressure, and used again for the washing. Since the same solvent is used in both stages, the Working up of the laden washing liquids can be carried out together so that the process is simplified considerably.

The washing in the two stages is preferably carried out at room temperature. In the first stage atmospheric or only slightly, for instance up to 1.5 atmospheres, in-

creased pressure is used. The pressure is determined by.

avoided in practical operation in view of sucking in air and having to compress a mixture of acetylene and oxygen which might cause danger of explosion. If the acetylene-containing gas has been obtained by a process which sure, for example to atmospheric pressure, and also by gassing out with the aid of pure acetylene, for example acetyleneobtained from the process, and if desired by further gassing out at elevated temperature and/or at reduced pressure. It is advantageous to use several stages when degassing and to remove first the gases which have a lower solubility coefficient than acetylene.

The washing liquid freed from acetylene is returned to the two Washing stages. It is preferable to branch ofi a small portion and to remove therefrom, for example by distillation, the constituents absorbed thereby which are not separable by degassing. .The washing liquid thus purified, if desired togetherwith a part of the liquid which has only been degassed, is used for the preliminary washing in the first stage. r

The washing liquid withdrawn from the first stage, without previous degassing, can also be freed by distillation from the constituents not separable bydegassing and returned to the'two Washing stages either alone or together with degassed Washing liquid.

. The invention will now be described with reference to the accompanying drawings which illustrate diagrammatically by Way of example three embodiments of the pro cess according to this invention. Similar parts are designated by similar letters in each of the drawings.

Referring. to Figure 1, an acetylene-containing gas mixture is led at atmospheric pressure through a pipe A into a washing tower B into which a solvent. for acetylene is charged at the top through a pipe C. The solvent laden with impurities and some acetylene leaves the washing tower B through a pipe R which conducts it toward the degassing tower O. r

, The preliminarily purified gas mixture is, led from the In the r The lower pressure limitis mainly dependent upon economic considera The upper necessary in the tower -B through atpipe -D-.to a'compressor Zfrom whichv it passes into a washing tower E. The bulk of the solvent for the acetylene is supplied to this tower through a pipe The laden washing li'quid' is withdrawn through' a pipe H andle'd into' a: re'ctificatihn tower I- 'while being released frorn pressure through; an-ae-xpansion' valve V.

In' thi's tower there takes place a separation of the-gases dissolvedin the washing liquidiinto' pure acetylene" which is withdr awr'r-througlr a pipe M and gases witha smaller solubility coefiicient:thanizacetylene which escape through a pipe"-L"'* and are suppli'ed to the compressor Z.

The washing'Lliquidileaves.the tower I through a pipe N" and; after 'it hasbeen= coinbinedr with the washingliquid flowing fromsthe preliminary washing towerB throughf'the pipe-R; passes-"to-the degassing tower O. From this the residual gas escapes through a pipe K and is le'd into the; lower." part. of' the rectification tower I.

The: constituents which 1 have-a higher solubility coetfi-- cient than 'acetylene escapefronr thezdegassing tower through a pipe The washing liquid freed from; acetylene and other readily. soluble' constituentsl leaves the degassing tower Ovthrough a pip'etQand passes through pipes F and C v to thewashing-towers-E and B.

Figure 2 shows 'the' sameprocessbut in which a part of: the degassed washingliquid, leaving the degassing tower O, is branched off, freed in" the vessel S from sulis't anees" which-have not been removed by the de-' gassing (theseaare withdrawn: through a pipe U) and sup' plied through :pipes T and G. to the first washing stage B. The portion of the: washing liquid which has only. been degassed and-which leaves-the degassing tower 0 through the pipe Q, is led to the second Washing stage E and'partlygto the firsbwashingnstage B.

According to'-'Figur-e'"3; the-washing:liquidhladen in the first'washing stage is led I through the'pipe R, if desiredtogether with-a-po'tt-iohofthewashing liquid leaving-,thedegassing tower O, to the treatment plant S and thence, after separation of the constituents not removable by] degassing, tothe washing stages E and B together with the washing liquid which has only been.

degassed from thedegassing ftower 0..

T he following examples, given with reference to Figure 2-,- will further illustrate this invention but'the invention is not restricted to'these examples. Parts are parts by weight unless otherwise'specifieda Example 1 By incomplete combustion of methane a gas mixture of'the following average percentage-by volume compo sitionis produced:

In addition" the mixture contains the following contaminants lIl' grams per cubic meter:

Acenaphthylene I U:sing 'a plant system as illustrated in Figure 2 of the dlag'rar'rima'tic'drawingannexed 100 cubic meters of the said ga's is passed'thr'oughdine A into the pre-washer B at a pressure of 1.1 atmospheres absolute and a tempera= tu'fe of 19 o.-z lewgranrrofsutyrelaemne being simultaneouslyfed in through line C. From line D a gas of the following average percentage-by volume composition is withdrawn:

Acetylene 8.14 C H -hydr0carbonS 0.1 Diacetylene l l 0.11 Benzene 0.02 Ethylene 0.3 Methane r 4.1" Carbon dioxide 35 Oxygen 01 Carbon monoxide 26.0 Hydrogen 56.73 Nitrogenplus argon 0.9

In addition the gas containstherfollowingsubstances in grams per cubic meter:

Phenylacetylene 0.09 Naphthalene. circa 0.02 Acenaphthene 0.01' Acenaphth'ylene: 0.01

As'a result',1a'bbnt 10% of'diacetylene, about 20-30% of" benzeneand phenylacet-ylene, about of naphthalene and'at'le'ast 90%' ofacenaphthene' and acenaphthylene have been" removed.

The'pre-washed gasis coinpressed to a'pressure' of9 atomsphe'resabs'olut'eina compressorZ'; The compressor" andthe? condensers attached'to' it" remain perfectly'clean;

apart from-afaint film ofcarbon black, even afteran operation'fonweeks; while in, the absence of a pre-wa'sh' stage deposits' 'of 5 carbon black'and' naphthalene will form after a few hours in the-cornpressor and especially in" thec'onden's'er's' resulting in"a'--decrease-'in the efiiciency of. tlic'ompres's'or' ah'd the" cooling effect of the condensers" after a twe weeks operation? Thesedepo'sitscan-onlybe removed by mechanical means.-

The g'asmixture compressed "to 9'atr'riospheres absolute then'passes-t'o the scrubber E into which 1150 kilograms of'butyrolactone are fedoverhead through line F at a temperature of 23 C'. Through line G 91 cubic meters of a gas having-the following average percentage-"by volume composition arewithdrawn:

Acetylene 0.1 Ethylene 0.3 Methane 4.5 Carbon dioxide 3-.8 Oxygen 0.1; Carbon monoxide 28.3 Hydrogen d 61.8 Nitrogen plus 'argon 1.1.

No polycyclic hydrocarbons and higher acetylenes can be identified.

The washing agent laden with acetylene and part of the other constituentscontained'in the crude gas leaves" the. tower E through the pipe H and passes into the rectifica tion tower I and thence through the pipe N into'the degassing tower 0" whereby heating to C. r'e clucingthe pressure to 0.2 atmosphere the dissolved gases are set free. The liberated gases pass through the pipe K into the lower end of the rectification column in which they flow in counter-current to the solvent. A part of' the acetylene with the gases expelled from the solution leave the tower I through the pipe L andare supplied to the suction side of the compressor 7.9 cubic: meters of acetylene which contains about 0.1% of C H -hydrocarbons less'than 0.1% of carbon dioxide, less than 0.02% of cliacetylene and less than 0.01% of benzene, are withdrawn through the pipe M. No polycyclic hydrocarbons can be identified. The gas constituents of..bet'- ter solubility than acetylene escape from the degassing tower 0 through the'pipe P. In the said gas, in addi tion t'o small quantitiesof acetylene, the'following com positions are detected: methylacetyl'ene, relatively large proportions of diacetylene, phenylacetylene, naphthalene, acenaphthene, and acenaphthylene.

The solvent which has been degassed in the degassing tower O is for the most part returned to the washer B through the pipe Q while a smaller partial stream is subjected to a distillation in the tower S. The solvent distilled over, after condensation and cooling, is returned through the pipe T to the tower B and if desired supplemented by solvent from the pipe Q. The impurities incapable of distillation in the tower S are withdrawn through the pipe U.

Example 2 By incomplete combustion of methane a gas mixture of the following average percentage-by volume composition is produced:

Acetylene 8.65 C H -hydrocarbons 0.1 Diacetylene 0.17 Benzene 1 0.08 Ethylene 0.3 Methane 5.2 Carbon dioxide 3 6 Oxygen 0.12 Carbon monoxide 24.9 Hydrogen 55.8 Nitrogen plus argon 1.1

In addition the mixture contains the following contaminants in grams per cubic meter:

Phenylacetylene 0.21 Naphthalene 0.36 Acenaphthene 0.10 Acenaphthylene 0.27 Pyrene 0.001

Using a plant system as illustrated in Figure 2, 100 cubic meters of the said gas are passed through line A to the pre-washer B at a pressure of 1.05 atmospheres absolute and a temperature of 25 C., 4.9 kilograms of N-methylpyrrolidone being supplied through line C. The gas withdrawn from line D has the following average percentage-by volume composition:

In addition the mixture contains .the following contaminants in grams per cubic meter:

Phenylacetylene 0.15 Naphth ene 0.03 Acenaphthene 0.01 Acenaphthylene 0.01 Pyrene not identifiable.

As a result, about 30% of diacetylene, of benzene and of phenylacetylene and about 90% of naphthalene, of acenaphthene and of acenaphthylene have been removed.

The gas mixture is then compressed to 13 atmospheres absolute in the compressor Z. Both the compressor and the condensers attached thereto, apart from a faint film of carbon black, remain perfectly clean even after an operation for weeks.

The compressed gas mixture is then scrubbed with 450 kilograms of N-methylpyrrolidone in the scrubber E. The result is substantially the same as that obtained in Example 1, except that 8.4 cubic meters of acetylene with about 0.1% of C H -hydrocarbons, less than 0.1% of carbon dioxide, less than 0.01% of diacetylene and less than 0.005% of benzene are obtained.

We claim:

1. An improved process for the separation of acetylene from a gas mixture containing acetylene and obtained by cracking hydrocarbons which comprises washing said gas mixture containing polycyclic hydrocarbon contaminants in a first stage with an amount of acetylene-absorbing solvent and at a pressure between about atmospheric and 1.5 atmospheres, which amount and pressure are suificiently low that only a small quantity of acetylene and diacetylene but the bulk of said contaminants is absorbed, washing the gas from the first stage in a second stage with a larger amount of the same solvent and at a pressure between about 8 and 30 atmospheres so as to absorb substantially the remainder of said acetylene, removing substantially pure acetylene from the solvent used in the second stage, combining said solvent freed of acetylene with the solvent from the first stage, the latter containing a small quantity of acetylene and diacetylene and said polycyclic hydrocarbon contaminants, removing the absorbed substances from the combined first stage and second stage solvent, and recycling the solvent substantially free from absorbed substances to said first and second stages for further washings.

2. A process as claimed in claim 1 wherein the pressure in the first stage is of the same range as the pressure under which the acetylene containing gas mixture has been obtained.

3. A process as claimed in claim 1 wherein the amount of solvent employed in the first stage is less than 2 percent of the amount of solvent employed in the second stage.

4. A process as claimed in claim 1 wherein the solvent employed is butyrolactone.

5. A process as claimed in claim 1 wherein the solvent employed is N-rnethylpyrrolidone 6. A process as claimed in claim 1 wherein the removal of absorbed substances from the combined first and second stage solvent includes a degassing, at least part of the degassed solvent returned to the second stage washing, the remaining degassed solvent distilled to remove absorbed constituents not separable by degassing, and the distilled solvent returned to the first stage.

7. An improved process for the separation of acetylene from a gas mixture containing acetylene and obtained by cracking hydrocarbons which comprises Washing said gas mixture containing polycyclic hydrocarbon contaminants in a first stage with an amount of acetylene-absorbing solvent and at a pressure between about atmospheric and 1.5 atmospheres, which amount and pressure are sufliciently low that only a small quantity of acetylene and diacetylene, but the bulk of said contaminants are absorbed, washing the solvent from the first stage in a second stage with a larger amount of the same solvent and at a pressure between about 8 and 30 atmospheres so as to absorb acetylene, rectifying the solvent from the second stage to free pure acetylene, degassing the rectified solvent from the second stage, distilling at least part of the solvent from at least one of the two stages to free absorbed constituents not separable by degassing, and reusing both degassed and distilled solvent for washing in each of the two stages.

References Cited in the file of this patent UNITED STATES PATENTS 2,714,940 Milligan Aug. 9, 1955 2,719,601 Bartholome et al. Oct. 4, 1955 2,726,734 Nirenberg Dec. 13, 1955 2,741,332 Finneran et a1 Apr. 10, 1956 2,762,453 Alexander Sept. 11, 1956 

1. AN IMPROVED PROCESS FOR THE SEPARATION OF ACETYLENE FROM A GAS MIXTURE CONTAINING ACETYLENE AND OBTAINED BY CRACKING HYDROCARBONS WHICH COMPRISES WASHING SAID GAS MIXTURE CONTAINING POLYCYCLIC HYDROCARBON CONTAMINANTS IN A FIRST STAGE WITH AN AMOUNT OF ACETLYLENE-ABSORBING SOLVENT AND AT A PRESSURE BETWEEN ABOUT ATMOSPHERIC AND 1.5 ATMOSPHERES, WHICH AMOUNT AND PRESSURE ARE SUFFICIENTLY LOW THAT ONLY A SMALL QUANTITY OF ACETYLENE AND DIACETYLENE, BUT THE BULK OF SAID CONTAMINANTS ARE ABSORBED, WASHING THE SOLVENT FROM THE FIRST STAGE IN A SECOND STAGE WITH A LARGER AMOUNT OF THE SAME SOLVENT 